ppc64 sbrk returns executable heap in 32-bit emulation mode
schwab at linux-m68k.org
Mon May 16 18:49:29 AEST 2016
Alan Modra <amodra at gmail.com> writes:
> On Thu, May 12, 2016 at 03:41:09PM +0200, Florian Weimer wrote:
>> We noticed that on ppc64, the sbrk system call in the 32-bit subsystem
>> returns executable memory. I assume it is related to this, in
>> * Unfortunately the PLT is in the BSS in the PPC32 ELF ABI,
>> * and needs to be executable. This means the whole heap ends
>> * up being executable.
>> #define VM_DATA_DEFAULT_FLAGS32 (VM_READ | VM_WRITE | VM_EXEC | \
>> VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
>> What is the rationale for this? This comment must be *really* old,
> I think the comment is just plain wrong. ppc32 needs an executable
> stack because it builds trampolines on the stack to support calling
> nested functions. I presume that's why the heap is executable.
The stack and the heap are separate mappings.
> I'm wrong about heap+stack needing the same protection then I can't
> think of any reason to require an executable heap.)
The heap and the BSS initially share the same page.
Andreas Schwab, schwab at linux-m68k.org
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